From: Aaron Schrab <aaron@schrab.com>
Date: Tue, 27 Nov 2012 23:30:17 GMT
Subject: Re: Possible vulnerability to SHA-1 collisions
Message-ID: <20121127233016.GC3937@pug.qqx.org>
In-Reply-To: <20121127230753.GA22730@sigill.intra.peff.net>

At 18:07 -0500 27 Nov 2012, Jeff King <peff@peff.net> wrote:
>PS I also think the OP's "sockpuppet creates innocuous bugfix" above is
>   easier said than done. We do not have SHA-1 collisions yet, but if
>   the md5 attacks are any indication, the innocuous file will not be
>   completely clean; it will need to have some embedded binary goo that
>   is mutated randomly during the collision process (which is why the
>   md5 attacks were demonstrated with postscript files which _rendered_
>   to look good, but contained a chunk of random bytes in a spot ignored
>   by the postscript interpreter).

I don't think that really saves us though.  Many formats have parts of 
the file which will be ignored, such as comments in source code.  With 
the suggested type of attack, there isn't a requirement about which 
version of the file is modified.  So the attacker should be able to 
generate a version of a file with an innocuous change, get the SHA-1 for 
that, then add garbage comments to their malicious version of the file 
to try to get the same SHA-1.